The present invention relates generally to MR imaging and, more particularly, to a method and apparatus for reconstructing panoramic and/or zoom MR images.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1 ) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or xe2x80x9clongitudinal magnetizationxe2x80x9d, M Z, may be rotated, or xe2x80x9ctippedxe2x80x9d, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received by an RF coil assembly and subsequently processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx Gy and Gz ) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
Typically, the RF coil chosen for a particular clinical application is selected as a function of the anatomy to be imaged in a field-of-view (FOV) or volume-of-interest (VOI). Often, a large FOV/VOI image is first acquired of the subject and then the user or technician then identifies a smaller region on the image for which an image of higher resolution or zoom is sought. For example, the larger FOV/VOI image may be acquired with a phased array coil having four coils or detection elements. To acquire data for an image with higher resolution of a smaller region or FOV/VOI, a different phased array coil consisting of four smaller coils is positioned and activated to acquire data for the higher resolution image of the specific FOV/VOI. This procedure can be cumbersome for the user and may be uncomfortable for the patient.
It would therefore be desirable to have a system and method capable of acquiring a large FOV/VOI image as well as acquiring data for an image with higher resolution of a smaller FOV/VOI without having to physically change coils on the patient.
The present invention solves the aforementioned problems and provides a system and method of reconstructing panoramic and/or zoom MR images. An RF coil assembly having a number of detection elements is provided. The RF coil assembly is designed such that the number of detection elements exceeds the number of data acquisition channels of the MR system. Accordingly, the detection elements may be grouped into a number of sets wherein each set transmits acquired data to a specific data acquisition channel or, alternately, only one set of detection elements may be activated wherein each detection element of the set transmits data to a data acquisition channel. As a result, a panoramic and/or zoom image may be reconstructed.
Therefore, in accordance with one aspect of the present invention, an RF coil assembly of an MRI system having plural data acquisition channels is provided. The RF coil assembly includes plurality of detection elements and a control to activate a given number of detection elements from the plurality of detection elements to acquire data of a first ROI, wherein the given number of detection elements exceeds the number of data acquisition channels of the MRI system. The control is further configured to transfer the data from the given number of detection elements across the number of data acquisition channels.
In accordance with yet a further aspect of the present invention, a method of MR imaging a subject includes the step of positioning the subject to be scanned in an imaging bay of an MR system having an RF coil assembly and-a number of data acquisition channels. The RF coil assembly has a plurality of detection elements exceeding the number of data acquisition channels of the MR system. The method further includes the step of activating a specific number of detection elements in an RF coil assembly to acquire imaging data from a first ROI and reconstructing an image of the first ROI. A second ROI within the first ROI is identified from the image of the first ROI and fewer than the specific number of detection elements in the RF coil assembly are activated to acquire imaging data from the second ROI.
In accordance with another aspect of the present invention, an MRI apparatus includes a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field. The apparatus also includes an RF transceiver system and an RF coil assembly to acquire MR images. The RF coil assembly includes a number of detection elements. The MRI apparatus further includes a number of data acquisition channels connected to the number of detection elements wherein the number of detection elements used to acquire imaging data is capable of exceeding the number of data acquisition channels.
In accordance with yet another aspect of the present invention, a computer readable storage medium having stored thereon a computer program to effectuate image reconstruction is provided. The computer program has a set of instructions that when executed by a computer causes the computer to initiate acquisition of MR data for a first ROI of the subject. The computer is then caused to receive MR data for the first ROI from a number of data acquisition channels of an MRI system. The MR system includes an RF coil assembly having a plurality of RF detection elements wherein the plurality of RF detection elements exceeds the number of data acquisition channels. The computer is then caused to reconstruct an image of the first ROI. A user input identifying a second ROI within the first ROI is received and fewer detection elements than used to acquire MR data of the first ROI are activated so as to acquire MR data of the second ROI using an identical RF coil assembly used to acquire the MR data of the first ROI.